Signal amplifier and magnetic disk storage apparatus using the same

A magnetic disk storage apparatus comprising:

• a storage medium for storing information;
• a drive unit rotating the storage medium and setting a potential of the storage medium with a first reference voltage;
• an arm having a first end and a second end;
• a read head of a magnetoresistance effect element which is mounted on the first end of the arm so as to read the information on the storage medium, the read head having a first note coupled to receive a first reference voltage and a second node for outputting a read signal representing the information on the storage medium;
• a controller chip which is mounted on the second end on the arm;
• and
• a signal amplifier chip which is mounted on the arm between the first end and the second end and which is coupled to the first and the second node of the head and is coupled to the controller chip, the signal amplifier chip including:
• a load element having a first end coupled to receive a second reference voltage and a second end,
• a first MOSFET of a first conductivity type having a gate terminal coupled to the second end of the read head, a drain terminal coupled to the first reference voltage, and a source terminal,
• a second MOSFET of a second conductivity type different from the first conductivity type having a gate terminal, a drain terminal coupled to the second end of the load element and generating an amplified signal on the read signal, and a source terminal coupled to the source terminal of the first MOSFET, and
• a first bias circuit providing a first bias voltage to the gate terminal of the second MOSFET.